1. Field of the Invention
The invention relates generally to the field of multiple transmitter message transmission systems, and more particularly to a multiple transmitter message transmission system utilizing a common communication channel for message distribution throughout the system and message delivery to a portable communication receiver.
2. Description of the Prior Art
Multiple transmitter message transmission systems have been widely used for the delivery of analog and digital messages. Once such prior art multiple transmitter message transmission system in wide use today is a simulcast transmission paging system which transmitted analog voice and digital data messages to a plurality of portable communication receivers, such as paging receivers operating within the system. Such prior art communication systems have utilized multiple transmitters to provide transmission coverage for large geographic areas, such as a large metropolitan area. FIG. 1A shows an electrical block diagram of the central transmitter facility 100 for a prior art paging system. Messages were inputted into the system by a user, generally through a telephone interconnect 102 for connection to the PSTN (public switched telephone network). As the messages were received in the system, they were processed by a paging terminal, which encoded the received messages for transmission. The encoded messages were then generally stored in a queue in a memory 106 prior to transmission. Prior to the actual transmission of the stored messages, the stored messages were recalled from memory 106 by the controller 108 and then distributed to each of the remote transmitter stations 120, as shown in FIG. 1B. The distribution of the recalled messages was accomplished using dedicated phone lines coupling the remote transmitter stations to the central transmitter facility, or as shown in FIGS. 1A and 1B, through the use of dedicated RF (radio frequency) or microwave link transmitter 110 located at the central transmitter facility and a dedicated RF or microwave link receiver 112 located at each remote transmitter station 120. The distribution channel utilized in the prior art systems was distinct from that of the paging channel used to deliver the messages to the paging receivers. As the messages were received at each of the remote transmitter stations 120, the remote transmitter station transmitter 116 was keyed by the site controller 118 while the central transmitter station transmitter 114 was being keyed by the central transmitter station controller 108. Delay equalization was provided at the central transmitter station transmitter 114 and the remote transmitter station transmitters 116 to allow simulcast transmission of the messages. The use of link transmitters and receivers in the prior art transmission systems added to both the complexity of the transmission system and to the cost of the transmission system. In addition, because a second RF channel was required for the link transmissions, licenses for two RF channels were required. In large metropolitan areas where a large number of RF channels were in use, it was often difficult, if not impossible, to obtain the required licenses to establish new paging services. There is a need to provide a multiple transmitter message transmission system which reduces the complexity and the cost of the system, and which also reduces the number of channels required for the operation of the paging system.